Only drop content mime types for unsubscribed collections.
Only drop content mime types for unsubscribed collections.

They were accidentally also dropped for collections hidden by resource
or mimetype filters, causing for example KMail not to allow creation of
sub-folders in them.

kolab-groupware/akonadi,kolab-groupware/akonadi,kolab-groupware/akonadi,kolab-groupware/akonadi